A conventional door closer of the type described comprises a door closer body having oil sealed therein, a piston housed in said door closer body and associated with the rotation of a door through an arm, a coil spring housed in said door closer body and urging said piston in the door closing direction, the arrangement being such that during door opening and closing operations, the oil pushed by the piston flows into a chamber disposed rearwardly as viewed in the direction of piston movement. Such a door closer is designed for fine adjustments so that the rate of flow of oil pushed by piston movement during door closing operation is lower than during door opening operation; thus, the door is braked during door closing operation. The aforesaid piston is connected to said arm through gears housed in the door closer body. More concretely, the rotary shaft of the gear is connected to the arm and the gear is meshed with the piston.
In the conventional door closer arranged in the manner described above, since the door closer body has gears and piston housed therein in their meshed state and has oil sealed therein and since fine adjustments are made so that the rate of flow of oil pushed by piston movement during door closing operation is lower than during door opening operation, the overall construction is complicated and the door closer body must be finished so that it is of sealed construction, thus offering a problem that the cost is high. Further, in the aforesaid conventional door closer, when opening the door, it is necessary to apply two forces, one required to open the door against the force of the coil spring and the other required to cause the piston to push the oil; thus, much force is required to open the door. Therefore, there has been a problem that the door opening load is high.